Semiconductor integrated circuit and design method thereof

ABSTRACT

In a layout process of a semiconductor integrated circuit, a power supply is initially formed in an arrangement in which the current threshold value is not exceeded. In a case where the excess over the current threshold value occurs after the power supply is formed, the power supply arrangement is changed according to the current threshold value, design rule data base, and power supply wiring density so as not to exceed the current threshold value.

BACKGROUND OF THE INVENTION

The present invention relates to a power supply structure and a powersupply design method of a semiconductor integrated circuit forspecifying a part where electromigration (EM) may occur and for reducingthe incidence of EM in a layout process of the semiconductor integratedcircuit having a multilayer interconnection configuration.

Conventionally, in a power supply design in a layout process of asemiconductor integrated circuit, a ring power supply may be formed of apair of power supply VDD and ground VSS positioned such that the pair ofpower supply VDD and ground VSS are surrounded by IO terminals. In thiscase, in order to simplify a wire arrangement process, one layer is usedin a vertical direction and another layer is used in a horizontaldirection.

FIG. 1 shows ring power supplies and a power supply wiring arrangementbetween an IO and the ring power supplies of a conventionalsemiconductor integrated circuit. Referring to FIG. 1, ring powersupplies 3 and 4 are positioned such that the ring power supplies 3 and4 are surrounded by an IO terminal region 1. The vertical direction ringpower supplies 3 and the horizontal direction ring power supplies 4 areconnected each other by vias (contacts) 5. Here, the inner ring isdesignated as VDD and the outer ring is designated as VSS. However, VDDand VSS may be reversed. In order to avoid a short circuit, a layer of apower supply wire 7 connecting the vertical direction ring power supply3 with a power supply (VDD) terminal 2 is formed of a layer differentfrom a layer of the vertical direction ring power supply 3. Likewise, inorder to avoid a short circuit, a layer of a power supply wire 6connecting the horizontal direction ring power supply 4 with anotherpower supply (VDD) terminal is formed of a layer different from a layerof the horizontal direction ring power supply 4.

In FIG. 1, the layer of the vertical direction ring power supply isdesignated, for example, as Mx, and the layer of the horizontaldirection ring power supply is designated, for example, as Mx−1. In thiscase, in order to avoid a short circuit, the power supply wire 7connected between the IO and the vertical direction ring power supply(Mx) is the layer designated as Mx−1, and the power supply wire 6connected between the IO and the horizontal direction ring power supply(Mx−1) is the layer designated as Mx.

As to the current threshold value of each layer, an upper layergenerally has a current threshold value higher than that of a lowerlayer (Mx>Mx−1). Therefore, the power supply wire thorough which thegreatest magnitude of current flows between the IO and the ring powersupply must be the upper layer. Otherwise, a current exceeding thecurrent threshold value flows through the power supply wire.Consequently, EM may occur which causes breaking of wire (In FIG. 1, acritical part where breaking of wire may occur is indicated by referencenumber 7).

In order to cope with this problem, following measures against EM havebeen taken: broadening the width of a wire between the IO and the ringpower supply, and increasing the number of vias.

Meanwhile, the maximum wire width of each layer reduces as processminiaturization advances. Therefore, a plurality of thin power suppliesare generally arranged in mesh form. Considering the worker-hour, it hasbeen common that a mesh power supply and a strap power supply have aconstant pitch (see Japanese Laid-Open Patent Publication No. 7-283378).

In this case, an arrangement position of a macro, a power supplyarrangement inside the macro or the like causes a part to where asufficient number of contacts can not be provided. Also in such casewhere the sufficient number of contacts can not be provided, the currentthreshold value of the via is exceeded. Consequently, the possibility ofthe EM incidence increases.

To cope with the problem, it has been proposed that the via is providedwith a reservoir as a measure against EM (see Japanese Laid-Open PatentPublication No. 2003-318260).

In recent years, semiconductor process miniaturization has been rapidlyincreasing the number of circuits (functions) integrated on a chip.However, decrease in the number of terminals is slower than increase incircuit integrity resulting from the process miniaturization. Therefore,the number of cases is increasing that the number of terminalsdetermines the chip size.

In many cases, the number of power supply terminals is reduced in orderto reduce the total number of terminals. When the number of power supplyterminals is reduced, problems arise such as voltage drop and EM.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a power supplyarrangement reducing the incidence of EM and to reduce the worker-hourrequired for producing the power supply arrangement.

To achieve the above-mentioned object, according to the first invention,a power supply wire is formed in a layout step for a semiconductorintegrated circuit such that the power supply wire between an IO and thering power supply is initially formed of a top layer (Mx), and in a casewhere a part of the power supply wire forms a short circuit with thering power supply, the ring power supply is formed of a layer (Mx−1)which is one level lower than the top layer.

According to the second invention, a power supply wire is formed in alayout step for a semiconductor integrated circuit such that a pair ofring power supplies VDD and VSS are crossed at a corner, and a powersupply IO is positioned at the corner, so that the power supply wirebetween the IO and the ring power supplies is formed of a top layer (Mx)without changing the conventional arrangement of the ring power supply.Note that, it is the current value that determines whether or not thepower supply wire is formed of the top layer.

In the third invention, a means for evenly supplying power to asemiconductor circuit is further provided to the arrangement accordingto the above-mentioned second invention.

According to the fourth invention, a power supply wire is formed in alayout step for a semiconductor integrated circuit such that the powersupply wire from a power supply IO is branched into a plurality of wiresand connected to a ring power supply so as to uniformly distribute thecurrent density.

According to the fifth invention, in the fourth invention, the powersupply wire between the power supply IO and the ring power supply isformed of a plurality of wire layers and the plurality of wire layersare connected by vias so as to more uniformly distribute the currentdensity compared with the fourth invention.

According to the sixth invention, a power supply wire is formed in alayout step for a semiconductor integrated circuit such that a pluralityof adjacent power supply wires having the same potential may be used toconnect a power supply IO with a ring power supply, and in this case,the adjacent power supply wires having the same potential are arrangedin mesh form so as to uniformly distribute the current density.

According to the seventh invention, in the sixth invention, the powersupply wire between the power supply IO and the ring power supply isformed of a plurality of wire layers and the plurality of wire layersare connected by vias so as to more uniformly distribute the currentdensity compared with the fourth invention.

The eighth invention is a combination of the fourth invention and thesixth invention.

According to the ninth invention, in the eighth invention, the powersupply wire between the power supply IO and the ring power supply isformed of a plurality of wire layers and the plurality of wire layersare connected by vias so as to more uniformly distribute the currentdensity compared with the fourth invention.

The tenth invention is to provide a method for changing a power supplyarrangement so as not to exceed the current threshold value, in a casewhere a ring power supply and a power supply wire between an IO and thering power supply are formed, for example, in a conventionalarrangement, and the current threshold value is exceeded in a part ofthe power supply wire.

The eleventh invention is to provide a method for preventing theoccurrence of EM. In the method, a power supply wire is first formed ina power supply wire formation step, and then the current threshold valueis checked. In a case where there is a possibility of the excess overthe current threshold value due to the number and shape of contacts onthe power supply wire, an appropriate number and shape of contacts arechosen. Forming contacts in this manner prevents the occurrence of EM.

The twelfth invention is to provide a method for preventing the excessover the current threshold value. In the method, a power supply and acontact are initially formed in a power supply forming step, and then apower supply arrangement in a macro, IP or the like is connected with aconstant pitch power supply arrangement of a chip. In connecting thepower supply arrangement and the constant pitch power supplyarrangement, there may be a possibility that the excess over the currentthreshold value occurs due to a contact formed unintentionally. In suchcase, the number of vias is changed or an unnecessary via is deleted inthe part having the possibility of the excess over the current thresholdvalue.

The thirteenth invention is to provide a method for detecting a regionin which a sufficient number of contacts can be formed and thesufficient number of contacts does not cause the excess over the currentthreshold value, and in a case where the same situation occurs as in thetwelfth invention, instead of correcting the number of contacts,changing a position of a constant pitch power supply of a chip.

The fourteenth invention is to provide a method for changing the wirewidth, wire length or layer of a current threshold value exceeding partof the wire so as not to exceed the current threshold value, and toreduce the possibility of the incidence of EM, in a case whereapplication of methods described in the eleventh through thirteenthinventions does not eliminate a current threshold value exceeding partof the wire.

According to a method of the fifteenth invention, in the tenthinvention, a position or width of the wire is changed so as not toexceed the predetermined wiring density.

The ring power supply and the wiring arrangement between the IO and thering power supply of the semiconductor integrated circuit according tothe first invention allows significant reduction of the incidence of EMat a part through which the greatest magnitude of current flows.Moreover, the arrangement does not involve area damage, such as increasein the number of wires.

According to the second invention, it is possible for a wire layerbetween the IO and the ring power supply to be formed of a layer havinga high current threshold value without changing the conventional ringpower supply arrangement. Therefore, it is not necessary to change thelayer of the ring power supply and the total number of vias decreases.Consequently it is possible to avoid a jam of wires.

According to the third invention, it is possible to evenly supply powerto a semiconductor integrated circuit while EM is reduced and a jam ofwires is avoided.

According to the fourth invention, it is possible to uniformlydistribute the current density at a part at which a wire from the powersupply IO is connected with the ring power supply, and to reduce theincidence of EM.

According to the fifth invention, a part at which a wire from the powersupply IO is connected to the ring power supply is lined with aplurality of layers so as to uniformly distribute the current density.Therefore, the fifth invention is possible to reduce the incidence of EMmore than the fourth invention reduces the incidence of EM.

According to the sixth invention, adjacent wires having the samepotential may be used, and in this case, these adjacent wires areconnected in mesh form between the power supply IO and the ring powersupply so as to uniformly distribute the current density. Therefore, thesixth invention is possible to reduce the incidence of EM more than thefourth invention reduces the incidence of EM.

According to the seventh invention, a part at which a wire from thepower supply IO is connected to the ring power supply is lined withlayers. Therefore, the seventh invention is possible to reduce theincidence of EM more than the sixth invention reduces the incidence ofEM.

According to the eighth invention, the current density on a part of awire connected to the ring power supply and on the wire between thepower supply IO and the ring power supply is uniformly distributed.Therefore, the eighth invention is possible to reduce the incidence ofEM more than the fourth and sixth inventions reduce the incidence of EM.

According to the ninth invention, a part at which a wire from the powersupply IO is connected to the ring power supply is lined with layers.Therefore, the ninth invention is possible to reduce the incidence of EMmore than the eighth invention reduces the incidence of EM.

According to the tenth invention, it is possible to reduce theworker-hour required for the subsequent steps of, for example,correcting the power supply incompliant with the current threshold valueand rearranging the wires.

According to the eleventh invention, a part having a high possibility ofthe EM incidence is previously specified, and a measure is taken to thepart, so that it is possible to reduce the worker-hour required for thesubsequent steps of, for example, correcting the power supplyincompliant with the current threshold value, and rearranging the wiresas well as reducing EM.

According to the twelfth invention, a part incompliant with the currentthreshold value caused by a layout change is specified, and a measure istaken to the part, so that it is possible to reduce the worker-hourrequired for the steps of, for example correcting the power supply, andrearranging the wires as well as reducing EM.

According to the thirteenth invention, it is possible to reduce theworker-hour required, for example, for reducing EM, for improving powersupply to a macro, IP or the like, for the subsequent steps ofcorrecting the power supply incompliant with the current thresholdvalue, and rearranging the wires.

According to the fourteenth invention, it is possible to reduce theworker-hour required, for example, for reducing EM, for improving powersupply to a macro, IP or the like, for the subsequent steps ofcorrecting the power supply incompliant with the current thresholdvalue, and rearranging the wires.

In the conventional art, a specification for the wiring density ischecked in a subsequent step. However, according to the fifteenthinvention, the specification is checked in advance. Consequently, arepeat step is omitted.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view illustrating a ring power supply arrangement in asemiconductor integrated circuit in conventional art.

FIG. 2 is a plan view illustrating an example of a ring power supplyarrangement in a semiconductor integrated circuit according to theinvention.

FIG. 3 is a plan view illustrating another example of a ring powersupply arrangement according to the invention.

FIG. 4 is a plan view illustrating still another example of a ring powersupply arrangement according to the invention.

FIG. 5 is an enlarged plan view illustrating still another example of aring power supply arrangement according to the invention.

FIG. 6 is an enlarged plan view illustrating still another example of aring power supply arrangement according to the invention.

FIG. 7 is an enlarged plan view illustrating still another example of aring power supply arrangement according to the invention.

FIG. 8 is an enlarged plan view illustrating still another example of aring power supply arrangement according to the invention.

FIG. 9 is an enlarged plan view illustrating still another example of aring power supply arrangement according to the invention.

FIG. 10 is an enlarged plan view illustrating still another example of aring power supply arrangement according to the invention.

FIG. 11 is a design flow chart for a semiconductor integrated circuitaccording to the invention.

FIG. 12 is a plan view illustrating an example of a power supplydesigned according to the flow chart in FIG. 11.

FIG. 13 is a plan view illustrating a power supply in the middle of thedesign process according to the flow chart in FIG. 11.

FIG. 14 is a plan view illustrating an arrangement of the power supplyin FIG. 13 which is corrected according to the flow chart in FIG. 11.

FIG. 15 is a plan view illustrating an arrangement of the power supplyin FIG. 13 in which wiring pitch is changed according to the flow chartin FIG. 11.

FIG. 16 is a plan view illustrating an arrangement of the power supplyshown in FIG. 15 in which wire width is changed according to the flowchart in FIG. 11.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 2 shows a ring power supply and a power supply wiring arrangementbetween an IO and the ring power supply according to the presentinvention. Compared with the conventional art arrangement shown in FIG.1, the power supply wire 7 running between the IO and the ring powersupply, which is the layer (Mx−1) in FIG. 1, is replaced with a powersupply wire 9 running between the IO and the ring power supply, which isthe upper layer (Mx). Moreover, in order to avoid a short circuitbetween a ring power supply 8 of the upper layer (Mx) and the powersupply wire 9 running between the IO and the ring power supply, a part10 of the ring power supply 8 susceptible to a short circuit is changedto the layer Mx−1.

According to the arrangement shown in FIG. 2, a part 9 having thelargest current value between the IO and the ring power supply can beformed of the upper layer having a high current threshold value. Thisarrangement achieves the effect of reducing the incidence of EM.

FIG. 3 shows another example of a ring power supply arrangementaccording to the present invention. FIG. 3 shows an IO terminal region11, power supply terminals 12, VDD/VSS metal ring power supplies (Mx)13, VDD/VSS metal ring power supplies (Mx−1 or Mx+1) 14, vias (contacts)15 connecting the VDD/VSS metal ring power supplies (Mx) 13 with theVDD/VSS metal ring power supplies (Mx−1 or Mx+1) 14, and power supplywires (Mx) 16 connecting the power supply terminals with the metal ringpower supplies. Compared with the conventional arrangement shown in FIG.1, in the arrangement in FIG. 3, the ring power supplies 13 and 14 ofVDD and VSS are crossed at a corner (circulated by broken line). In thiscase, VDD comes outside in a horizontal direction wiring part, and VSScomes outside in a vertical direction wiring part. Now, vertical wires13 of the ring power supply are formed of a top layer (Mx), andhorizontal wires 14 of the ring power supply are formed of a layer(Mx−1) which is one level lower than the top layer (Mx). VDD and VSS maybe reversed.

According to the arrangement shown in FIG. 3, the ring power supplies 13and 14 have a step (level difference) at a corner. The power supplyterminal 12 is positioned such that the power supply terminal 12 alignswith the step at the corner. In this arrangement, the wire 16 having thehighest current value between the IO and the ring power supply can beformed of the top layer (although it is the current value thatdetermines whether or not the wire is formed of the top layer).Consequently, this arrangement achieves the effect of reducing theincidence of EM.

FIG. 4 shows still another example of a ring power supply arrangementaccording to the present invention. In FIG. 4, the power supplyterminals 12 for VDD and VSS are positioned such that each of the powersupply terminals 12 aligns with the step at each corner of the ringpower supplies 13 and 14. In this arrangement, power is supplied fromfour corners of a chip. Therefore, it is possible to evenly supply powerto a semiconductor integrated circuit, while the wire 16 between the IOand the ring power supply remains to be the top layer.

FIGS. 5-10 are enlarged views illustrating techniques used to improvethe power supply wire 7 connecting the power supply terminal 2 with thehorizontal direction ring power supply 3 at the left side in FIG. 1.

In FIG. 5, a wire from the power supply IO is branched into two wires.In FIG. 5, the power supply IO is connected with the ring power supplyin one-to-two manner instead of one-to-one manner. That is, in thisarrangement, a current flow path is branched. In this arrangement, it ispossible to prevent concentration of the current flow on the ring powersupply and to uniformly distribute the current flow. Consequently, theincidence of EM is reduced.

In FIG. 6, the wire between the power supply IO and the ring powersupply shown in FIG. 5 is lined with layers. This improves the thresholdcurrent density of the wire connected between the power supply IO andthe ring power supply. Consequently, the incidence of EM is more reducedin FIG. 6 than in FIG. 5.

FIG. 7 shows a wiring diagram in which three wires having the samepotential are connected between the power supply IO and the ring powersupply in mesh form. In this arrangement, the threshold current densityis improved more than in the arrangement in which the power supply IO isconnected with the ring power supply in one-to-one manner. Therefore, itis possible to reduce the incidence of EM.

In FIG. 8, the wire between the power supply IO and the ring powersupply shown in FIG. 7 is lined with layers. This increases thethreshold current density of the wire connected between the power supplyIO and the ring power supply. Consequently, the incidence of EM is morereduced in FIG. 8 than in FIG. 7.

FIG. 9 is a combination of the arrangements shown in FIG. 5 and FIG. 7.The power supply IO is connected with the ring power supply inone-to-two manner instead of one-to-one manner. That is, in thearrangement in FIG. 9, the current flow path is branched. Moreover, thewires between the power supply IO and the ring power supply are arrangedin mesh form. This arrangement has a threshold current density higherthan that of the arrangement in which the power supply IO is connectedwith the ring power supply in one-to-one manner. In this arrangement, itis possible to prevent concentration of the current flow on the ringpower supply and to distribute the current flow. Consequently, it ispossible to significantly reduce the incidence of EM.

In FIG. 10, the wire between the power supply IO and the ring powersupply shown in FIG. 9 is lined with layers. The wire from the powersupply IO to the ring power supply is lined with the layers, so that itis possible to improve the threshold current density of the wire betweenthe power supply IO and the ring power supply. Consequently, theincidence of EM is more reduced in the arrangement in FIG. 10 than inthe arrangement in FIG. 9.

In the arrangements shown in FIG. 6, FIG. 8, and FIG. 10, the wire 7 islined with layers and connected by vias (not shown).

FIG. 11 is a design flow chart for a semiconductor integrated circuit inaccordance with the present invention. FIG. 11 shows a floor planforming step 17, a power supply forming step 18, a coarse positioning(fine positioning) step 19, an EM check step 20, a current thresholdvalue table 21 of each layer, a design rule 22, a wiring density checkstep 23, a power supply arrangement correction step 24, and a wiringstep 50. In FIG. 11, a power supply is first formed in step 18. Then,referring to the current threshold value table 21 of each layer, acurrent threshold value exceeding part of the layer is specified. Thecurrent threshold value table 21 and the design rule 22 are used toperform the wiring density check step 23. Next, in the power supplyarrangement correction step 24, a power supply arrangement compliantwith the current threshold value, the design rule, and the wiringdensity is realized. A specific example of the design method accordingto FIG. 11 is explained below.

FIG. 12 shows an example of a power supply designed according to theflow chart shown in FIG. 11. Referring to FIG. 12, a method is explainedfor connecting a power supply with an object, such as a block, a macroand IP, having its own internal power supply to be connected. FIG. 12shows an outer frame 25 of a macro, mesh power supplies or strap powersupplies 26-29 of a chip, power supply patterns 30 and 31 inside themacro, and contacts 32 and 33 connecting the power supplies of the chipwith the power supply patterns inside the macro.

In FIG. 12, on the macro and on the IP, power supply wires 26 and 27 tobe used in the chip are formed at a constant pitch 40. After forming thepower supply wires and before forming the contact, a part having apossibility of the excess over the current threshold value is specified.In a part where only a contact incompliant with the current thresholdvalue and the design rule can be formed (the power supply patterns 30and 31 in the macro in FIG. 12), no contact is formed but a part inwhich the current threshold value is not exceeded (contacts 32 and 33 onthe wires 28 and 29 in FIG. 12) is formed. According to this method, theparts 30 and 31 having a possibility of the excess over the currentthreshold value are eliminated in advance. Therefore, it is possible toreduce the worker-hour required for the subsequent steps of, forexample, correcting the power supply and rearranging the wires due tothe excess over the current threshold value.

FIG. 13 is a plan view illustrating a power supply in the middle of thedesign process according to the flow chart in FIG. 11. FIG. 14 shows anarrangement in FIG. 13 which is corrected according to the flow chart inFIG. 11. As shown in FIG. 13, the power supply wire is first formed, andthen, contacts are provided for all connection points. Next, the flowchart shown in FIG. 11 is applied so as to delete contacts 34 and 35causing the excess over the current threshold value and a contactcausing a DRC error. The result is shown in FIG. 14. Compared with themethod described with reference to FIG. 12, the method described withreference to FIG. 13 is effective when a layout has to be changed. Thatis, this method is effective for a part incompliant with the currentthreshold value or the design rule any longer, due to, for example, achange in an arrangement of the macro, power supply wiring rule, orcurrent value caused by a layout change.

FIG. 15 shows the arrangement in FIG. 13 whose wiring pitch is changedaccording the flow chart shown in FIG. 11. FIG. 15 shows changed chippower supply pitches 41 and 42, displaced chip power supplies 36 and 37,and contacts formed for the displaced chip power supplies 38 and 39.

When the above-mentioned measure does not eliminate a current thresholdvalue exceeding part, the constant pitches (40 in FIG. 13) between thepower supply wires (26 and 27 in FIG. 13) are changed so as to displacea chip-side power supply such that contacts compliant with the currentthreshold value can be formed (wires 36 and 37 in FIG. 15). This methodenables to eliminate contacts (34 and 35 in FIG. 13) having a highincidence of EM, while sufficient power is supplied from the powersupply to be used in the chip to the macro and the IP. It is notnecessary that the changed chip power supply pitches 41 and 42 are thesame.

In an arrangement shown in FIG. 16, the wire width shown in FIG. 15 ischanged according to the flow chart shown in FIG. 11. When theabove-mentioned measure does not eliminate a current threshold valueexceeding part, the width of wires (36, 37, 28, and 29 in FIG. 15) isbroadened (as indicated by reference numbers 43 and 44 in FIG. 16). Inaddition to broadening the wire width, the total number of contacts isincreased (from the number of contacts indicated by reference numbers 38and 39 in FIG. 15 to the number of contacts indicated by referencenumbers 45 and 46 in FIG. 16). According to this method, it is possibleto reduce the worker-hour required for the steps of reducing theincidence of EM, improving power supply to the macro or IP, correctingthe power supply and rearranging the wires in a case where the currentthreshold value is exceeded.

In the conventional art, a specification for the wiring density ischecked in a subsequent step. However, according to the flow chart shownin FIG. 11, the specification is checked in the wiring density checkstep 23 in advance. Consequently, a repeat step is omitted.

As described above, a semiconductor integrated circuit and a designmethod thereof according to the present invention allow reduction of theincidence of EM with the reduced worker-hour required for the designmethod, so that the semiconductor integrated circuit and the designmethod of the present invention find utility, for example, in asemiconductor integrated circuit having a multilayer interconnectionconfiguration, and in the layout design thereof.

1. A semiconductor integrated circuit having an arrangement in which, ina power supply designing step of a layout process, metal layers areprovided on one side of a ring power supply.
 2. A semiconductorintegrated circuit having an arrangement in which, in a power supplydesigning step of a layout process, a power supply source and a ringpower supply are connected within a top layer without changing a layerof the ring power supply.
 3. A semiconductor integrated circuit setforth in claim 2, further including an arrangement which evenly suppliespower to a chip.
 4. A semiconductor integrated circuit having anarrangement in which, in a power supply designing step of a layoutprocess, a connection between a power supply source and a ring powersupply is formed such that a wire from the power supply source isbranched into a plurality of wires and connected to the ring powersupply.
 5. A semiconductor integrated circuit set forth in claim 4having an arrangement in which, the connection between the power supplysource and the ring power supply is formed by a plurality of metallayers, and the plurality of metal layers are connected by vias.
 6. Asemiconductor integrated circuit having an arrangement in which, in apower supply designing step of a layout process, a connection between apower supply source and a ring power supply is formed such that a wireis connected with adjacent power supply wires in mesh form and connectedto the ring power supply.
 7. A semiconductor integrated circuit setforth in claim 6, having an arrangement in which, the connection betweenthe power supply source and the ring power supply is formed by aplurality of metal layers, and the plurality of metal layers areconnected by vias.
 8. A semiconductor integrated circuit having anarrangement in which, in a power supply designing step of a layoutprocess, a connection between a power supply source and a ring powersupply is formed such that a wire is connected with adjacent powersupply wires in mesh form and connected to the ring power supply, andthe wire is branched into a plurality of wires and connected to the ringpower supply.
 9. A semiconductor integrated circuit set forth in claim8, having an arrangement in which, the connection between the powersupply source and the ring power supply is formed by a plurality ofmetal layers, and the plurality of metal layers are connected by vias.10. A design method of a semiconductor integrated circuit comprising thesteps of: specifying a current threshold value exceeding part between anIO terminal which is a power supply source and a ring power supply, andforming a power supply wire between the IO terminal and the ring powersupply, and changing and connecting a layer of the power supply wireaccording to the current threshold value of the layer.
 11. A designmethod of a semiconductor integrated circuit set forth in claim 10,wherein an optimal contact is chosen and used depending on a shape ofcontacts having different current threshold values, and on the number ofvias.
 12. A design method of a semiconductor integrated circuit setforth in claim 10, further comprising the steps of: performing aconnection of the power supply regardless of the current thresholdvalue, the shape of contacts, and the number of vias, specifying acurrent threshold value exceeding part, and changing the number of viasor deleting vias according to the current threshold value of a layer.13. A design method of a semiconductor integrated circuit set forth inclaim 10, wherein a connection between a block, such as a macro or IP,having its own internal power supply pattern and a chip power supplyhaving a constant pitch power supply pattern is formed such that in acase where a current threshold value exceeding part presents, theconstant pitch power supply pattern of the chip power supply is changedso as to ensure a sufficient number of contacts.
 14. A design method ofa semiconductor integrated circuit set forth in any one of claims 11-13,wherein in a case where the methods set forth in claims 11-13 do noteliminate a current threshold value exceeding part, the position, width,or length of the chip power supply is changed so as to realize a layoutcompliant with the current threshold value.
 15. A design method of asemiconductor integrated circuit set forth in claim 10, wherein a changeand connection of the layer of the power supply wire connected betweenthe IO terminal and the ring power supply is performed in considerationof wiring density.